According to the report, the vehicle was in autonomous mode and in the far right lane of a main thoroughfare in the California city of Mountain View. As it approached a red light, the car automatically signaled that it would make a right turn. Cars in the same lane ahead of the autonomous vehicle were waiting at the red light to proceed straight, so the autonomous vehicle got to the right of the lane to pass those other cars, but it sensed some sandbags around a storm drain in the road, and it stopped.

As the light turned green, the autonomous vehicle tried to drive back to the center of the lane to get around the sandbags. The autonomous vehicle’s operator saw a bus approaching in the left-hand mirror “but believed the bus would stop or slow to allow the Google AV [autonomous vehicle] to continue,” the report said.

“Approximately three seconds later, as the Google AV was reentering the center of the lane it made contact with the side of the bus,” the report continued. “The Google AV was operating in autonomous mode and traveling at less than 2mph, and the bus was traveling at about 15mph at the time of contact.”

The autonomous vehicle was a Lexus that Google had tricked out with sensors. The car suffered a damaged left front fender and left wheel, as well as a broken sensor on the driver’s side door.